This invention relates to electrical connectors, particularly to a self-terminating coaxial tap connector for use with an external termination element.
Coaxial cables and connectors typically have a center conductor insulated from and surrounded by a shield. Coaxial cables and connectors are often used for high frequency electrical signals, since the coaxial design provides a more uniform electrical impedance, and the surrounding shield prevents electrical signals from radiating into or out of the inner conductor. Coaxial connectors, when coupled, are designed to maintain these characteristics of uniform impedance and shielding of the center conductor.
A coaxial "tap" connector is connected between two coaxial cables in order to "branch" or "tap" the signal in an additional third direction. A tap connector is often used to add an additional device to a coaxial bus or local-area-network running between several devices. A coaxial "tap" connector has two coaxial connector ports having connected shields and connected center conductors, with a "tap" or "T" connection to the connected center conductors for carrying the signals in yet a third direction. Commonly, the tap connection crosses through and ends outside of the connected shields for connection to a printed circuit board.
When a coaxial connector on a cable or on a coaxial tap connector is left "open" or unconnected, the uniform impedance characteristics are disturbed, and undesirable reflection of signals and radiation of electrical signals into and out of the center connector can occur. A "self-terminating" coaxial connector reduces these problems by automatically switching to a "terminated" condition when the coaxial connector is left open or uncoupled. A terminated condition exists when the center conductor is connected to the shield through a termination circuit element having the same characteristic impedance as the coaxial connector and cable.
One type of self-terminating coaxial connector is shown in U.S. Pat. No. 4,575,694 to Lapke et al. Lapke et al shows a connector to be used on the end of a coaxial cable which switches to a terminated condition when the connector is uncoupled or disconnected from a compatible (matching) connector. Lapke et al discloses a sliding dielectric sleeve disposed in the connector shell for movement between a first position and a second position which moves a switch element to include or exclude a termination circuit element. The sliding dielectric sleeve is biased by a coil spring in the shell behind the sleeve, and movement of the sleeve is driven by abutment with the face of a compatible connector during the coupling of two compatible connectors. Unfortunately, the design of Lapke et al leaves a substantial portion of the center conductor extending beyond the point of connection to the termination element inside the connector. This extension can cause both the reflection and signal radiation problems earlier described. Also, the design of Lapke et al requires a large number of moving mechanical elements to be assembled within the connector body, greatly increasing the cost and reducing the reliability of the connector.
A second type of self-terminating coaxial connector is shown in co-pending U.S. patent application Ser. No. 07/369,382, filed 06/21/89 and entitled SELF-TERMINATING COAXIAL TAP CONNECTOR (as amended) on which the present applicant is a co-inventor. In a first embodiment, this invention shows a self-terminating coaxial connector port which uses a sliding dielectric element to move a switch contact away from the center conductor. A second embodiment, without a sliding dielectric element, uses abutment with the mating connector to move a switch contact away from a contact land which runs through a termination circuit element to the center conductor. However, these designs also suffer from the presence of a extension or connection to the center conductor beyond the point of termination which can cause the reflection and signal radiation problems earlier described. Also, the designs require a number of mechanical elements to be assembled within the connector body, greatly increasing the cost and reducing the reliability of the connector.